Pretty much what it says on the tin:

It's the beginning of 2016. Due to a fast-spreading virus, humans have lost the ability to reproduce themselves. The virus makes current artifical fertilization techniques useless as well. As a result, the population starts decreasing, due to the complete lack of newborns.

Now, how much time would be needed to have a 10% decrease of the population, assuming 7 billion people living on Earth before the crisis?

A bit of backstory on the question

I wrote a story which started with this premise and tried - without much success - to figure out how much time would have humans to "react" and actively find a cure before the population drop becomes so severe that:

  • strategic facilities (like power plants, food production chains...) starts being abandoned due to lack of personnel;
  • only medical laboratories are mantained active in order to try to find a cure, while the rest of the research is stopped or diverted to solve the problem.

Since if I had asked this, it would have been probably too broad/opinion based (correct me if not), I have resorted to the question in italics, in order to reduce the scope.

I hope the question is both answerable and on topic. If not, feel free to point it out.

  • $\begingroup$ the movie Children of Men could be relevant for an idea of the society we would be in $\endgroup$
    – WoJ
    Commented Jul 13, 2018 at 16:44

10 Answers 10


Well, to begin with, the negative economic impact wouldn't even begin until, say 20 years later, which is when the missing newborns would have become seriously productive in society. Prior to that, the economic impact might have been positive, as all the money that would have gone into feeding and educating the missing newborns is, instead, available for other things.

It's the psychological impact that would hit the world like a meteor. Suddenly, our species has lost its future. Newlyweds ask themselves; what is my marriage for, if there will be no family to raise? All older-than-newborn children currently in adoptive care will be snatched up by parents who no longer have the option of producing their own children.

To answer your question about the workforce, according to these statistics (http://www.dop.wa.gov/SiteCollectionDocuments/Reports/2009_State_Workforce_Report_Pages/WorkforceAge.html) they would probably start really feeling the pinch in about 40 years, IMO. Prior to that there would be adjustments (the average worker age would be rising rapidly). Workers who would previously have been retired are instead, persuaded to continue for as long as they can do their jobs.

However, the bigger issue is not whether there are enough workers to man the power stations but whether there are enough women of child bearing age to be able to repopulate the world.

If they discover a cure after 20 years, the world will have suffered a blow but it can recover, albeit with many changes to the way society functions. We've lost a huge chuck of population but the lack has not yet cut into our childbearing population.

After 30 years we've lost ten of our prime years (physically speaking) but the world could recover, especially if very young women bear children to be raised by older parents.

After 40 years we've probably only got 15% of the population who is young enough to reproduce. That's down from maybe 50%. And even worse, women over 40 have a much harder time giving birth and there is a much higher rate of birth defects (https://en.wikipedia.org/wiki/Advanced_maternal_age). At this point there will be a general collapse of some sort, though it may not happen for another decade or two.

If they discover a cure after 50 years, they will have passed the point of no return for civilization as we know it. Most women are too old to conceive. Even if they do, by the time these children are 30 most of the older generation will be dead or senile. Or society depends greatly on the information which is passed down through the education system, but even more on the experience of coworkers and peers, gained through work experience.

By the time sixty year have passed, all the workers will be old. Many of them will be suffering from physical and mental disabilities but may be continuing to work because there are no replacements. Society will have given up. There may be scientists still working on a cure even though they know it will do us no good. Mass suicide and other effects of hysteria and depression will further disrupt what is left of our civilization.

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    $\begingroup$ "the negative economic impact wouldn't even begin until, say 20 years later..." What about the daycare and education industries? Manufacturers of diapers, car seats, toys, etc? $\endgroup$
    – djs
    Commented Sep 25, 2015 at 21:51
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    $\begingroup$ @djs For macroeconomic purposes they would be canceled out by increased demand on other industries. $\endgroup$
    – Random832
    Commented Sep 26, 2015 at 2:17
  • $\begingroup$ This answer is the best one in tie with @Avernum's! :D I really would like to mark both as an accepted answer :D I think I will have to choose one :/ $\endgroup$ Commented Sep 28, 2015 at 20:00

Based on some handy data from 2011, we can estimate worldwide deaths at around 55 million per year. At that rate, for 700 million people to die, you’d only have about 12.65 years.

Now, this annual death toll is definitely going to see some yearly variance based on current world conflicts, epidemics, natural disasters, etc. In general, I would not expect this to have a major effect on that estimate. However, you’re talking about a world where the existence of our species is now in serious jeopardy. Societies don’t handle existential threats very well. With almost half a million births every day, the medical community will notice this number plummet to zero very quickly. It is quite likely that there will be global unrest within a few months, if not weeks. Since we don’t have any historical precedents (fortunately) for “imminent” global existential threats, it’s difficult to say just how bad this would get. I think it is safe to assume that the worldwide death toll is going to increase, probably on the order of millions and then tens of millions. This will start to shrink that 12 year timeframe fairly quickly.

On a broader scale, how long would it take for humanity to be doomed? According to census.gov, there are over 600 million children in the 0-4 age bracket. Fertility in women peaks around the age of 31 and then steadily declines for the next decade. Women can continue to give birth in their forties, though this tends to require access to better medical care and has much higher risk to both mother and child. You could then reasonably suggest that we would have about 40 years, plus or minus a couple of years, to cure the virus and still be able to save the species.

Bear in mind, however, that this is going to be 40 years of lots and lots of unrest. Children will be particularly vulnerable during that period, so you may see a smaller percentage of those 600 million children surviving that long. Worse still, population distribution means a great many of those children are going to be in poorer nations with less access to the kind of healthcare that could help them continue to give birth into their forties.

If it takes you decades to find a cure, there’s going to be a major population decline. If it takes more than 40 years, humanity might not recover.

  • 7
    $\begingroup$ One more point, the intersection between the 10%-ish of people who are going to die in the next 12.65 years, and the people operating strategic facilities, is fairly small. Especially in developed countries people expect a substantial retirement, and the death rate among people with jobs is rather lower than the death rate of the whole population including retirees. And whoever replaces those who die in post will be older than 12.65 years! So if it weren't for the general panic, despair and collapse of civilisation as we know it, 10% natural deaths in itself wouldn't hit key personnel. $\endgroup$ Commented Sep 25, 2015 at 19:28
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    $\begingroup$ I think the number of deaths would be a little less than 55 million per year because the 55 million probably also includes newborns who die every year $\endgroup$
    – Ovi
    Commented Sep 25, 2015 at 19:53
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    $\begingroup$ @Ovi That's a fantastic observation. It looks like there were 4.5 million infant deaths in 2015... that's a big difference. $\endgroup$
    – Avernium
    Commented Sep 25, 2015 at 19:58
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    $\begingroup$ It would take at least three months for the medical community to reach consensus that there is no more pregnant women in the world. If there is no fertilization starting today, there will still be births for the nine months ahead, so you have to add nine months to your 12.65 year figure. $\endgroup$ Commented Sep 25, 2015 at 20:43
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    $\begingroup$ Also, humanity won't be doomed if 40 years or more passes by. If female eggs are still functional, they can be frozen. You can add 20 more years (since there are several successful cases of births for mothers 60 years old). $\endgroup$ Commented Sep 25, 2015 at 20:45

A couple decades. The scientists would be searching for these things, simultaneously:

  1. Immune people. There are sure to be people somewhere that are immune to your retrovirus infection. (There are people immune to AIDS). If you find one young immune women (and probably track down her relatives), you can collect her eggs and start repopulating Earth with immune people. You could also use cloning techniques to produce a immune female zygote from a immune male cell.

  2. A way to remove retrovirus DNA insertions. This is not easy and there are people researching it for 30 years-ish already (this would cure AIDS). Maybe the breakthrough is near, since it is already being researched.

  3. You could use gene therapy to lock down the viral DNA inside the cells, converting it into an inert endogenous retrovirus (so it becomes inert and no longer activates - human genome has hundreds of these strands of DNA). A crafted virus that hunts the infertility virus.

  4. Uninfected people. Depending on your infection vectors, these can be more or less rare, but it is almost impossible for the virus to reach everyone. If you can secure uninfected people and make sure they do not get infected, humanity is saved. Some isolated community (like the Easter Island natives) might not have contact with the virus.

The world human population would take a huge drop, maybe half or more. Also the cure would have to be protected since every force able to mount an attack would try to seize it.

  • $\begingroup$ Point n°2 was the solution in the story, though following a "non-conventional" path ;) By the way, I agree on most of your points XD Strangely enough, in my story the virus mutated in several varieties which could pass to humans from several different animals, so point 4 would have some issues... but since this was not specified in the scenario, this is still a really good answer ;) $\endgroup$ Commented Sep 25, 2015 at 21:39
  • $\begingroup$ Your point 1 reminded me: of this en.wikipedia.org/wiki/The_Handmaid's_Tale_%28film%29 (actually I've never seen the film, only heard about it). $\endgroup$
    – celtschk
    Commented Sep 26, 2015 at 9:44
  • $\begingroup$ 5. Suspended animation. $\endgroup$ Commented Sep 26, 2015 at 14:08

Even after a cure is found, there would be on-going problems for many decades.

It would begin with a major, world-wide, baby-boom. Every couple who would have had children during the gap will start their family immediately. Many couples who want to have children in general but were procrastinating will also start their families immediately in case something similar goes wrong.

There will be only a few months to prepare maternity hospitals, recall and retrain midwives, obstetricians, and neonatal pediatricians, and train extra doctors and nurses in those fields.

There will be a little more time to build elementary schools, and train the teachers. It may be desirable to build some flexible schools that can be elementary schools for a few years, then middle schools, then high schools, then colleges. Similarly, many teachers will need to follow the boom along.

About 60 years after the cure, the boomers will start retiring.


Just on the reproductive aspect, you will have 30-40 years until the current newborn women are approaching the end of their potential childbearing years.

Much beyond that and potentially fertile wombs will mostly be gone.

  • $\begingroup$ Okay, but then how much time before a substantial decrease in population (of the order of 700 million - 1 billion people)? 50-70 years? $\endgroup$ Commented Sep 25, 2015 at 17:16
  • $\begingroup$ Anyway, maybe I have got your point: after 40 years, there wouldn't be any more possibility to have new children because there would be no women able to become pregnant. Is this what you wanted to say? $\endgroup$ Commented Sep 25, 2015 at 17:21
  • $\begingroup$ Yes, correct. This gives you a end to the window of being able to reverse it. My opinion of population drop, would be there would be extensive wars and internal unrest in countries that would result in massive casualties before you would need to worry about this, or about population drop from natural causes. $\endgroup$ Commented Sep 27, 2015 at 13:35

I would say the (human) world would have some 70 years or so before eternal night sets in on the species.

40 years as Michael Richardson has stated, for natural feminine pregnancy age. After this, all child bearing females would be history.

30 more years just in case scientists find a means to clone humans. So far the task has appeared impossible. If human cloning techniques are invented, then you get infinite timespan for the research as scientists could go on cloning the smartest minded people over and over again until they finally find a cure.

  • 1
    $\begingroup$ +1 for the human clonation idea. This was actually not considered, but it is something I have completely overlooked :D $\endgroup$ Commented Sep 25, 2015 at 17:41
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    $\begingroup$ Remember that so far human cloning has proven extremely difficult (virtually impossible). No effort in this regard has gone even a few steps towards success. The cell just won't form a blastula and would die off after dividing 2-4 times. $\endgroup$ Commented Sep 25, 2015 at 18:10
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    $\begingroup$ I would posit that a more fruitful use of research time after we hit the 40 year mark is artificial wombs versus cloning (assuming there is a set of frozen eggs/embryos that were not affected by the virus; the premise does not preclude this based on my interpretation) $\endgroup$
    – Foon
    Commented Sep 25, 2015 at 19:16
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    $\begingroup$ @Foon I disagree to the extent that there shouldn't be an either/or mentality at any point. All potentially viable options should be pursued in parallel. $\endgroup$ Commented Sep 25, 2015 at 20:56
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    $\begingroup$ We can clone sheep, cats and dogs that I know of. I suspect that the reason humans haven't been cloned is that it's ethically unacceptable, not that it's impossibly hard. Were cloning to be the only way to avoid extinction as a species, I expect those ethical objections would be overridden. Similarly, if genetic modification of human embryos offered any way out, I expect that GM mostly-humans would be created. If uninfected human embryos are available, their implantation in animal wombs might well be easier than artificial wombs. $\endgroup$
    – nigel222
    Commented Sep 27, 2015 at 21:54

Worldwide, overall current mortality rate is about 7.89 per 1000. This does not mean that people live over 100 years on the average. Due to population growth, there are more young people than would be true for zero population growth. By the time you reach age 100 about half of the remaining population will die each year.

Once the babies stop, the overbalance of young people starts decreasing. So the mortality rate starts to increase.

Deaths per 1000  /  Years to reach 6 billion

8 / 19
9 / 17
10 / 15
11 / 14

So, somewhere around 14-17 years seems most likely to me to reach 6 billion people.

In terms of research, etc. deaths in 3rd world countries do matter nearly as much as the industrial world based on the amount of medical research taking place. So this may not be the best measure of long research viability.

As despair and similar emotions could be widespread post baby-bust, I would expect suicide and homicide rates could easily rise a bit. Likewise the decreasing population could relieve food supply stress, lowering the mortality rate due to malnutrition.

Unless some crazy dictator think this is a perfect time to launch some nukes and increase the mortality rate dramatically, I think I cover the likely range.

I expect that some of the medical research into the baby-bust problem will have useful applications in treating disease, etc. -- If these are significant, they could more than offset the lack of youth in the population demographics. However, the idea that we have extended lifespan is often misunderstood. People in the middle ages did not die off in their mid thirties. Infant mortality, diseases and accidents killed off many people, but if you were able to avoid these common problems, you could easily live to be 80 or 90. Lengthening the average lifespan of medical researches and delaying menopause would have obvious potential benefits in this scenario.

Given that modern medicine has not really extended lifespan, I don't expect any sudden increases in lifespan. Research into telomeres suggests that potential lifespan expansion may be possible in the relatively near future, though perhaps not soon enough to help in this scenario.

  • $\begingroup$ Very interesting the discussion on the death rate changing with time according to the age ;) $\endgroup$ Commented Sep 25, 2015 at 17:43

A cure allowing the resumption of in vitro fertilization would also push the limit out beyond the ~40 years point cited by others for a recovery that only allowed natural birth. The current record for a successful IVF pregnancy is at least a 66 year old woman. There are at least two older claims; however the Wikipedia article explicitly states that the 70yo claimant is disputed due to the mother's lack of a birth certificate. By calling the 66yo woman the oldest verified mother, it implies a similar issue with a 69yo claimant.

However, maintaining much of the current/near future technology base would become increasingly problematic after a few decades because of the declining number of experts who'd remain alive to teach the next generation. Without major improvements in longevity and/or education and maintenance-free industry, an IVF-powered population recovery might occur concurrent with or shortly be followed by a collapse of much modern society due to a loss of the skilled people needed to maintain it.


Round about year 20 would be when the uploading "Manhattan Project" achieves success so humans can transition to a fully artificial lifeform.

Some suggest that with worldwide resources and everyone with a basic IT knowledge working the problem from all possible directions it could be achieved in less than 10 years.

Don't forget that we also have modern genetics as well as saved copies of the human genome (all 3.5B base pairs) so growing a 3D cellular casting with a transplanted organic brain from a 70 year old is not totally unfeasible. last time I checked a kidney had been grown in a lab and tested. Also reversing mental decline using a combination of 8 different drugs as well as light therapy is feasible and has been tested.


If you are content with 10k or so survivors, never!

Procedure is as follows:

day 1: Space station is declared quarantine. All frozen embryos are declared quarantine, along with pre-existing frozen eggs and sperm.

year 1: Space station is being resupplied by sterilized food packages. Development in automation commences.

year 2: controlled breeding program established in space station (we are at serious risk of inbreeding now but it won't matter too much). The population growth has to be carefully controlled here, as a large population would be fatal to further plans.

year 3: sterilized nursery delivered to space station

year 10: beginning to divert resources from education to production

year 15: large hab modules delivered to space station

year 20: all further development proceeds on automation and AI platform

year 25: college & electronic library delivered to space station

year 30: mass rollout of solar technology

year 40: collection of internet library; space station supplies should be extended to +50 years by this point, space station boosted to +50 year orbit. Elderly care starts consuming economy

year 50: delivery of 100 long-lasting re-entry capsules to space station. Space station supplied to +70 years, including 3d printers and raw materials. Further resupplies about to cease.

year 51: collection of knowledge in libraries and long-lasting electronics should be completed. Elderly care overruns economy.

year 52: Space station is on its own.

year 60: Mass die-offs begin due to inadequate medical care

year 70: Embryo storage power supply is converted to RTGs.

year 80: Runaway mass die-offs has reduce quality of life to terrible levels.

year 120: Humans extinct on earth by this point. (Yes we have a few 120+ alive now, but without support they won't be). The disease is extinct with them.

year 121: The sixth generation returns from the space station. They can tap the remains of the automated systems to begin farming. Female population: 100

year 122: Crack open the first of the frozen embryos.

year 142: At maximum rate, female population: 500 (200 adults). This assumes that automation development worked and we can sustain this population boom. Once reaching this stage though, it's no longer a problem.

year 162: Runaway population boom subsides due to running out of frozen embryos. This brave new world has very few human-specific pathogens.

  • $\begingroup$ For your return plan, you'll have to hope that the virus won't survive without humans. $\endgroup$ Commented Sep 27, 2015 at 21:18
  • $\begingroup$ True. But, if it can survive and cannot be cured or blocked, you've got a problem so nasty that barring divine intervention I would give humans a negligible chance of survival. $\endgroup$
    – Joshua
    Commented Sep 27, 2015 at 21:37
  • $\begingroup$ How do you get the mothers to the space station after the outbreak starts? Assume an all-male crew (statiscally I think this is valid). $\endgroup$
    – Chris H
    Commented Sep 28, 2015 at 12:55
  • $\begingroup$ @ChrisH: Statistically, it's not. Last I checked there was something like a 75% chance of at least one female already there. $\endgroup$
    – Joshua
    Commented Sep 28, 2015 at 15:15
  • $\begingroup$ @Joshua, OK, that's higher than I thought but I can't find any stats. You've still got to get the facilities and skills for IVF, antenatal care and delivery into an environment where they haven't been done before. There will be novel risks to pregnancy in space. And don't forget the few years to decades of administrative dithering. $\endgroup$
    – Chris H
    Commented Sep 28, 2015 at 15:28

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